1. Field of the Invention
This invention relates to a method and an apparatus for pressing a sheet material, and is suitable for press machining a corrugated fin of a heat exchanger.
2. Description of the Related Art
Press machines for forming a continuous corrugated fin, having a continuous corrugated form, by pushing, from above and below, a group of punches onto a sheet material are known from Japanese Unexamined Patent Publication Nos. 2003-115567 and 2001-137960.
However, in the press machine according to Japanese Unexamined Patent Publication No. 2003-115567, each of the upper and lower punches constituted by an upper group of punches and a lower group of punches serially clamps and punches a sheet material with a good timing by using stepped cam plates to thereby execute press machining of corrugated fins. However, charging of the material and withdrawal of the product must be carried out, between the upper punch group and the lower punch group, before and after pressing.
In the press machine according to Japanese Unexamined patent Publication No. 2001-137960, however, pressing is conducted by controlling the vertical timing (press timing) of the group of punches, a feed amount of a material (sheet material) by a material feeder and its feed timing. In other words, because an independent material feeder for feeding the sheet material is necessary, productivity is low and the cost of the press machine is high.
Material conditions such as the thickness of the sheet material and the material of the sheet exert influences when the material feeder feeds the sheet material. Therefore, the sheet material is likely to slip, the fed sheet material undergoes deflection and the material slips when the group of punches clamp the material. For these reasons, the accuracy of the processed product is likely to drop.